Harvesters have headers (typically called “Draper platforms”) that carry cut crop material on conveyor belts. These conveyor belts extend across the width of the header to a central discharge region of the header. The conveyor belts are supported on rollers that, in turn, are mounted on header float arms that are elongated and extend forwardly. These arms are pivotally mounted to a frame of the header. The forward ends of the header float arms are coupled to and support a cutter bar that extends across the width of the header.
The cutter bar and/or the forward ends of the arms skid across the surface of the ground as the harvester goes through the field harvesting crop. As the harvester is driven through the field, the ground rises and falls underneath the header and the arms pivot up and down responsibly, thereby permitting the cutter bar to follow the contours of the ground more closely.
If the cutter bar and/or the front ends of the arms apply too much pressure to the ground they will dig into the ground and be damaged. Controlling the downforce is therefore important in keeping the header and harvester operating properly.
To reduce the downforce applied by the header to the ground, each arm is partially supported by a hydraulic, pneumatic, or mechanical spring. The springs are coupled to the frame of the header and transmit some of the crop weight to the frame. They do this by exerting a lifting or “up” force on the arms that counteracts the weight of the arms and the additional downforce exerted on the arms by the cut crop material that falls backward onto the conveyor belts after it is cut by the cutter bar. The springs transfer some of the weight of the header float arms and cut crop material to the feeder house on which the header is supported and transfer the weight off the cutter bar and ground.
The cut crop material is not evenly distributed across the width of the header conveyors. The crop is cut by the cutter bar across the entire front of the header and then falls backwards onto the conveyor belts, a left conveyor belt and a right conveyor belt. The left conveyor belt carries the cut crop material from the left side of the header to the center section of the header, and the right conveyor belt carries the cut crop material from the right side of the header to the center section of the header. Once the cut crop material reaches the center section of the header, the left and right conveyors dump the cut crop material into a center conveyor that carries the cut crop material backwards, through the feeder house, and into the self-propelled vehicle portion of the harvester.
Depending upon its position across the front of the header, each header float arm needs a different amount of upward counterbalancing force in order that each header float arm exerts the same downforce against the ground that all the other header float arms do. In the ideal situation, each header float arm provides the same, optimal downforce against the ground.
In order for each header float arm to provide the same downforce against the ground, each spring must apply a different upforce to its associated header float arms. This is necessary since different portions of the conveyor (and hence each header float arm) support different quantities of cut crop material. As the conveyors move laterally across the width of the header toward the lateral midpoint of the header, more and more cut crop material falls onto the conveyor belt. And the header float arms closer to the lateral midpoint of the header carry a greater and greater weight of cut crop material. This additional crop material resting on the header float arms closer to the lateral midpoint or center of the header means that the header float arms closer to the lateral midpoint require a greater counterbalancing upforce—the force exerted by the springs—if each header float arm is to apply a constant downforce against the ground.
What is needed, therefore, is a control system for applying to each header float arm in the header a counterbalancing upforce that is appropriate to support the crop load and to maintain constant the downforce exerted by each header float arm against the ground (either directly, or through the cutter bar). It is an object of this invention to provide such a system.